Agar-agar is a mixture of polysaccharides (agarose, agaropectin) of high molecular weight between 40,000 and 300,000. It is made generally by producing algae extraction juices by autoclaving and by treating the juices containing about 2% of agar-agar in order to extract the agar-agar.
Presently there are two main treatment types for the agar-agar juices and these are applied depending on the product quality which is desired, and in particular the chemical purity and bacterial contamination. To obtain a present day commonplace quality product which may be utilized in particular in the agrofoodstuff business, this treatment comprises adding sodium hypochlorite or sodium chlorite to the extraction juice in concentration of about 1% by weight, and then providing directly either a mechanical pressing of the gelled juice, or a congealing/decongealing of the gelled juice, so as to obtain an agar-agar cake which will be subsequently dried. However this product is slightly colored and contains minerals, so that it is unsuitable in fields demanding higher quality (medicine, pharmaceutics, biotechnology). However, this method does offer the advantage of economy.
To make a higher quality agar-agar product, the main treatment employed presently comprises adding chemical additives to the extraction juice, whereby it is possible both to remove the color from the juice and to precipitate the heavy cations Ca.sup.++, Fe.sup.+++, Mg.sup.++ etc. which are present in the extraction juice, and then to congealing/decongealing the extraction juice at low temperature (-20.degree. C.) so as to precipitate agar-agar of high quality. As a rule this operation is repeated to provide constant quality. However this process is exceedingly costly due to the energy required and this accounts for the present agar-agar prices, where for the high grade type the costs are about double those of the ordinary quality agar-agar.
Furthermore, in certain applications in science, analysis and biochemistry, the slight presence of sulfate in the agaropectin fraction of agar-agar presents a problem and presently it is eliminated by precipitating the agaropectin by means of complexing agents (ethylene glycol, cetylpyridinium chloride, etc.). However these complexing agents too are costly and cause the loss of the entire agaropectin fraction which amounts to 10 to 50% by weight of the entirety.
It has already been suggested in another technical field to treat agaroid solutions (strongly sulfated polygalactan close to the carrageenan family) be means of ion exchange resins: "Chemical Abstracts," vol. 74, Apr. 19, 1971 #16, page 71, abstract No. 77,673, D. T. lonescu, et al, "Decolorization of Agaroid Solutions by using Macroporous Anion Exchanger." This treatment places the agaroid solution in the presence of a cationic resin conditioned into ammonium form which in turn is placed in the presence of an anion resin, lastly by ending the decoloration on activated carbon. However this process is inapplicable to extracting high-grade agar-agar because the ammonium ion required to treat the agaroid (in view of the subsequent recovery procedure of the product by alcohol precipitation requiring the presence of an ammonium salt soluble in the hydro-organic phase) amounts to incompatible contamination pollution in the light of the quality sought for the agar-agar. The skilled artisan is well aware of this incompatibility, and this may explain why the two techniques have not been merged, the more so that the above cited article goes back to 1971.
Also, the decoloration quality of the agaroids is mediocre and is implemented on activated carbon, whih, for agar-agar removes any economic significance from such a process. Furthermore, in spite of a resemblance in terminology, agaroid has a very polar chemical structure (many sulfate groups are present), which differs strongly from the chemical structure of agar-agar: agaroid relates to the treatment techniques for the strongly sulfated phycocolloids, whereas agar-agar relates to the treatment techniques for weakly sulfated or neutral polysaccharides, and there is no relationship between the said techniques. Applying the process from one field to another or priori is not contemplated by the expert. Also, as a rule agaroid is precipitated in the final phase by an alcohol providing bacteriological decontamination, however this operation is very costly and in the case of agar-agar would render the obtained product more expensive than the high-grade products obtained by congealing/decongealing.
The object of the present invention is to provide a novel method for making agar-agar from algae extraction juices whereby it is possible to produce high-grade agar-agar compatible with applications in the medical, pharmaceutical and bioengineering fields.
One object of the invention is to keep production costs near those presently entailed by the production of commonplace quality agar-agar.
Another object is to produce desulfated agar-agar without losing a fraction of the agar-agar and without significant increases in costs.
A further object is to facilitate the recovery of the coloring by-products contained in the extraction juices for possible economic applications.